I'm using OpenBSD pf 4.6 or 4.7, but it is before the new changes. Anyway, I have a private LAN and a DMZ setup. My rules work for what I need and I'm not a pf expert by any means, but what rules do I need if I want an external user to be able to login to a server in my LAN?

For example, a user on the outside would login to 192.168.1.100 which is a Unix machine on my private LAN using ssh. I'd assume that is possible, but I have no idea how to implement it.

4.7 was where the big syntax change occurred for NAT. The 4.7 Upgrade Guide has a description of before and after rules which may help.

Note 1: PF has had continuous improvements in the years since you last upgraded or installed. These affect more than NAT. You may want to spend time with the PF User's Guide, which is aligned with syntax and best practices for OpenBSD 5.4-release.

Note 2: There are additional changes to PF for 5.5, including a completely new queuing subsystem to replace altq. OpenBSD 5.5 is planned for release on 1 May 2014.